Axial-piston machines such as pumps and motors are known which have a cylinder drum journaled for rotation in a housing such that the journaling for the drum, which defines the axis of rotation thereof, is fixed relative to the housing, i.e. the cylinder drum is not free to tilt relative to the housing.
Such an axial-piston machine can have a reversing device between an end face of this cylinder drum and a housing portion provided with at least one pressurized-fluid passage, whereby between the cylinder drum and this housing portion an intermediate disk (control disk) is transversely shiftable. The control disk can have a side, turned toward the housing, with a spherical curvature bearing against a correspondingly shaped counter surface of the housing portion.
The cylinder can, for example, be journaled by a pair of radial bearings upon a central shaft which can be fixed in a pivotal housing in the case of a variable-displacement machine or in a fixed housing in the case of a nonadjustable machine. Alternatively, the drum can be journaled in this housing and in a drive flange of the axial piston machine or, in still another alternative, in the drive flange and in a swingable slide. In the latter case, the cylinder drum is swingable relative to the housing and is supported slidably thereagainst. The cylinder drum can, however, be journaled also by a pair of roller bearings directly in the housing.
In such machines, either the parts receiving the bearings and those carrying the reversing surface must be fabricated with high precision so that the reversing surface lies precisely perpendicular to the axis of rotation of the drum or the parts carrying the reversing surface must be given play or freedom to move.
In the previously known machines with such adjustability, the center of curvature of the spherically curved surface of the two spherically curved surfaces on both sides of the intermediate disk lie along the axis of rotation of the cylinder drum. Through the spherically curved surface, the fluid passages extend and open, because of the curvature of the surfaces, in a direction which is not perpendicular to the axis of rotation of the drum.
As a consequence, the pressure in these fluid passages applies a force to the intermediate disk which has a component radial to the axis of rotation. The fluid from the pressure passage enters the gap between the two surfaces so that, within this gap, a pressure field is generated.
The pressure is effective perpendicular to the surface so that a resultant force is generated which for each unit area is effective in the direction of the center of curvature so that this force can be resolved into a force parallel to the axis of rotation of the cylinder drum and into a force perpendicular thereto.
If the pressure force integrated over the entire surface is considered, these components are found to include resultant or net forces which are applied to the intermediate disk in a lateral direction, i.e. tending to laterally displace this disk.
Such forces must be counteracted in conventional machines by engaging the disk from the exterior laterally. Since these forces are dependent upon the pressure of the liquid, the counterforces must also be dependent upon the fluid pressure to minimize distortion moments on the disk. These counterforces must be generated by the pistons which are pressurized by the working fluid.
When the intermediate disk has convex spherical surfaces, the compensating forces must be applied to the side of the disk opposite that which is provided with the pressure passage so that expensive fluid-guide passages must be used.
The intermediate disk must be secured so that it is not entrained with the cylinder drum by friction forces. So that this tendency to rotatably entrain the disk by the drum does not apply significant force to the disk, which would result in transverse forces in addition to the axial pressure forces applied by the drum, relatively complex devices are needed to prevent entrainment. Such machines are described in Japanese patent JA-PS 690826 (47-43243) and French patent FR-PS 73.29921.